The present invention relates to multiple pressure condensers for steam turbines, and, more particularly to means for suppressing overcooling of the condensate.
In steam turbine condensers, the heat extracted from the exhaust steam should be just sufficient to convert it into condensate. Further cooling below the saturation temperature of the exhaust steam should be avoided because energy must again be used during the feed water preheating in order to compensate for the heat losses associated with the overcooling and this additional use of energy has, naturally, a deleterious effect on the overall efficiency of the steam turbine installation.
In order to suppress this overcooling, it is known, in multiple pressure condensers, to heat the overcooled condensate in the low pressure and intermediate pressure part by exhaust steam from the high pressure part of the condenser. However, the overcooling can only be partially decreased by this means at appropriate economic expense because not all the high pressure exhaust steam condenses since a part of it will pass into the intermediate pressure part and the low pressure part. This is due to the unavoidable leakage between the condenser parts. The desired reduction in the heat consumption or improvement to the condenser vacuum cannot, therefore, be completely achieved in this way. Furthermore, this procedure involves the danger of erosion on the loops of cooling tubes due to effervescing condensate impinging on the cooling tubes.
A further method for suppressing the condensate overcooling consists in condensate originating from the low pressure part being caused to emerge in the intermediate pressure part as droplets, from a distributor plate, into exhaust steam derived from the high pressure part. In order to obtain the desired heating of the colder condensate, a rather large dropping height is necessary for the condensate droplets, which is structurally undesirable.
The same disadvantage applies to a method in which condenstate extracted from the low pressure part and the intermediate pressure part flows onto lower level inclined plates in the high pressure part, from whence it drains over a height of approximately 1.5 m into the hot well of the high pressure part and is heated by the high pressure exhaust steam during this process.
In a further known method, overcooled consensate is conveyed by a pump from the low pressure part into the high pressure part, atomized there and heated by the high pressure exhaust steam. The fault-prone rotating parts of the pump naturally imply a sacrifice of availability and this method is not recommended for this reason. To this must be added the further disadvantage that the energy necessary for driving the pump impairs the overall efficiency of the turbine installation.
Because of the higher operating costs resulting, condensate overcooling is very heavily penalized by the orderer of the installation, for example by one million sFr/1.degree. C. Attempts are therefore made to suppress overcooling completely.